Steel Alloying Elements Quiz

Alloying Elements

• Alloys are metallic substances made of two or more elements.
• Alloying elements are added to base metals to achieve specific properties not found in the base metal alone.
• Group 6 elements are common alloying elements.

Alloy Examples

• Steel (Fe & C): Used in appliances, vehicles, and construction.
• Cast Iron (Fe & C): Used in pipes, machinery, and car parts.
• Bronze (Cu & Sn): Used in bearings, sculptures, and coins.
• Brass (Cu & Zn): Used in instruments, electrical components, and fittings.
• Duralumin (Al & Cu): Used in the aviation and aerospace industries.

Steel Alloying Elements

• Carbon (C): Increases tensile strength and hardness, but decreases ductility, toughness, and machinability.
• Chromium (Cr): Increases tensile strength, hardness, hardenability, toughness, and resistance to corrosion and scaling at high temperatures.
• Cobalt (Co): Increases strength and hardness, and permits higher quenching temperatures, increasing red-hardness.
• Tungsten (W): Increases strength, hardness, and toughness, and has greater cutting efficiency at high temperatures.
• Copper (Cu): Negatively affects forge welding, but not significantly other types.Beneficial to atmospheric corrosion resistance at concentrations above 0.2%.
• Manganese (Mn): A deoxidizer, improves forgeability, increases tensile strength, hardness, and hardenability, decreases scaling and distortion, and increases carbon penetration in carburizing.
• Molybdenum (Mo): Increases creep resistance, strength, hardness, hardenability, and toughness, and strength at high temperatures. Improves machinability and resistance to corrosion. Increases red-hardness properties.
• Nickel (Ni): Increases strength and hardness without sacrificing ductility and toughness. It increases resistance to corrosion and scaling at elevated temperatures, particularly in high-chromium (stainless) steels.
• Phosphorus (P): Increases strength, hardness, and improves machinability, but adds brittleness to steel.
• Silicon (Si): A deoxidizer, increases tensile and yield strength, hardness, forgeability, and magnetic permeability.
• Sulfur (S): Improves machinability, but may cause brittleness at high heat, decreases weldability, impact toughness and ductility.
• Titanium (Ti): Forms carbides with carbon improving surface hardness and wear resistance. Prevents localized precipitation of carbides at grain boundaries.
• Niobium (Nb): Similar behaviour to Titanium, often more costly .
• Tantalum (Ta): Similar to Titanium, but with better thermal conductivity and higher melting point, and is also costly .
• Vanadium (V): Increases strength, hardness, wear resistance, and shock resistance, and enhances red-hardness.

Aluminum Alloying Elements

• Magnesium (Mg): Increases strength and improves work hardening ability.
• Copper (Cu): Increases strength, enables precipitation hardening, reduces corrosion resistance, ductility and weldability.
• Silicon (Si): Increases strength and ductility, and produces precipitation hardening in combination with magnesium.
• Zinc (Zn): Increases strength, enables precipitation hardening, and may cause stress corrosion.
• Lithium (Li): Substantially increases strength and modulus of elasticity, provides precipitation hardening, decreases density.
• Chromium (Cr): Increases stress corrosion resistance.
• Nickel (Ni): Improves elevated temperature strength.
• Titanium (Ti): Used as a grain-refining element.

Titanium Alloying Elements

• Aluminum (Al): Alpha stabilizer, improves strength, reduces density.
• Vanadium (V): Beta stabilizer, enhances strength and corrosion resistance.
• Molybdenum (Mo): Beta stabilizer, increases strength and toughness of titanium alloys.
• Zirconium (Zr): Improves corrosion resistance without significantly altering density.
• Iron (Fe): Occasionally added to improve strength and reduce manufacturing costs.

Nickel Alloying Elements

• Chromium (Cr): Enhances corrosion and oxidation resistance.
• Iron (Fe): Improves strength, and reduces cost. Forms basis of nickel-iron alloys (e.g., Invar, stainless steel).
• Molybdenum (Mo): Increases strength and corrosion resistance, particularly in harsh environments.
• Cobalt (Co): Enhances high-temperature strength and corrosion resistance. Used in superalloys for jet engines and gas turbines.
• Copper (Cu): Improves resistance to acidic environments and enhances thermal and electrical conductivity.
• Aluminum (Al): Increases oxidation resistance, and provides precipitation hardening.
• Titanium (Ti): Provides strength and facilitates precipitation hardening.
• Silicon (Si): Improves oxidation resistance and strength at high temperatures.
• Tungsten (W): Increases strength and creep resistance at high temperatures.
• Carbon (C): Adds strength and hardness but may reduce corrosion resistance.
• Boron (B): Improves grain boundary strength and high-temperature performance.
• Niobium (Nb): Improves strength, weldability, and corrosion resistance.

Copper Alloying Elements

• Zinc (Zn): Forms brass, enhances strength, corrosion resistance, and machinability.
• Tin (Sn): Forms bronze, improves hardness, wear resistance, and strength.
• Nickel (Ni): Increases corrosion resistance and toughness, often used in marine hardware.
• Aluminum (Al): Improves strength, corrosion resistance, and hardness in aluminum bronze alloys.
• Silicon (Si): Enhances wear resistance and machinability in silicon bronzes.
• Phosphorus (P): Refines grain structure and increases strength, particularly in phosphor bronze.
• Lead (Pb): Improves machinability, commonly added to brass alloys.
• Beryllium (Be): Creates beryllium copper, known for exceptional strength, conductivity, and corrosion resistance.

Glossary

• Machinability: Ease with which a material can be machined; specific energy, horsepower, or shear stress.
• Hardenability: How deep a metal can be hardened after heat treatment.
• Scaling: Formation of oxides on metal surfaces.
• Quenching: Strengthening metal by rapid cooling.
• Red-hardness Ability to retain a sufficient degree of hardness at high temperature.
• Carburizing: Process of absorbing carbon from a carbon-bearing material into iron or steel.
• Creep: Time-dependent deformation at high temperatures and constant stress.
• Precipitation hardening: A form of hardening in which extremely tiny particles of an alloying element are uniformly spread in the original material that increases strength and hardness.

Specific Alloying Element Questions

• Steel carbides (cheapest): Titanium (Ti).
• Duralumin: Aluminum (Al) & Copper (Cu).
• Brass workability: Lead (Pb).
• Manganese (steel): Reacts with sulfur, improving forgeability, increasing tensile strength, hardness, and hardenability, decreasing scaling and distortion, and increasing carbon penetration during carburizing.
• Lightest base alloying element: Aluminum (Al).
• High-temperature strength of nickel-based superalloys: Cobalt (Co).
• Invar: Nickel (Ni) & Iron (Fe).